68 OF THE SA.P, AND INSENSIBLE PERSPIRATION. 



and proves, for the most part, a clear watery 

 ^ liquor like the sap, and subject to similar 

 chemical changes. It is observed to be uni- 

 form in all plants, or nearly so, as well as the 

 sap, except where odorous secretions transude 

 along with it. Still there must be a very es- 

 sential difference between the original sap of 

 any plant and its perspiration, the latter no 

 longer retaining the rudiments of those fine 

 secretions which are elaborated from the for- 

 mer ; but that difference eludes our senses as 

 well as our chemistry. The perspiration of 

 some plants is prodigiously great. The large 

 Annual Sunflower, TIelianthus annuus, Ger- 

 arde Emac. 751. f. 1, according to Dr. Hales, 

 perspires about 17 times as fast as the ordi- 

 nary insensible perspiration of the human skin. 

 But of all plants upon record 1 think the Cor- 

 nelian Cherry, Corniis masculo, is most ex- 

 cessive in this respect. The quantity of fluid 

 which evaporates from its leaves in the course 

 of 24 hours, is said to be nearly equal to twice 

 the weight of the whole shrub. Du Hamcl 

 Fhys, des Arbres, v. 1. 145. 



